Calculation of Mass Concrete Temperature Containing Cooling Water Pipe Based on Substructure and Iteration Algorithm

Mathematical physics equations are often utilized to describe physical phenomena in various fields of science and engineering.One such equation is the Fourier equation,which is a commonly used and effective method for evaluating the effectiveness of temperature control measures for mass concrete.One important measure for temperature control in mass concrete is the use of cooling water pipes.However,the mismatch of grids between large-scale concrete models and small-scale cooling pipe models can result in a significant waste of calculation time when using the finite element method.Moreover,the temperature of the water in the cooling pipe needs to be iteratively calculated during the thermal transfer process.The substructure method can effectively solve this problem,and it has been validated by scholars.The Abaqus/Python secondary development technology provides engineers with enough flexibility to combine the substructure method with an iteration algorithm,which enables the creation of a parametric modeling calculation for cooling water pipes.This paper proposes such a method,which involves iterating the water pipe boundary and establishing the water pipe unit substructure to numerically simulate the concrete temperature field that contains a cooling water pipe.To verify the feasibility and accuracy of the proposed method,two classic numerical examples were analyzed.The results showed that this method has good applicability in cooling pipe calculations.When the value of the iteration parameterαis 0.4,the boundary temperature of the cooling water pipes can meet the accuracy requirements after 4∼5 iterations,effectively improving the computational efficiency.Overall,this approach provides a useful tool for engineers to analyze the temperature control measures accurately and efficiently for mass concrete,such as cooling water pipes,using Abaqus/Python secondary development.

Identification of the Diffusion Coefficients of Pollutants ( N O 3 - and Mn2+) through the Walls of Concrete Tank and Vulnerability of the Stored Water Quality

The populations of urban centers in Congo-Brazzaville have decided to develop various methods of water storage (concrete or masonry underground tanks) for domestic use, due to shortages in the distribution of water through the public network. However, questions remain as to the physico-chemical quality of the water stored in these tanks, when these structures are built in wet and relatively polluted areas. This paper presents a model of pollutant diffusion through the cementitious matrix (concrete) of tank walls simulated at a buried reservoir. The results of the experimental and numerical simulations show that certain concrete parameters, such as porosity, permeability and diffusivity, have a significant influence on the transfer of pollutants through the concrete walls, thus altering the physico-chemical quality of the stored water. The numerical models (1D) used to predict pollutant transfer and the quality of the stored water are consistent with those of the optimal control for identifying the diffusion coefficient. Major ion concentrations appear to be correlated with system porosity and diffusion coefficient. Nevertheless, the identification of the diffusion coefficient from the optimal control method, based on an explicit numerical resolution of a finite volume PDE for the approximation of the experiment, is not consistent with that of the optimal control method.

Water Stability Improvement of Acid Fine Aggregate-Based Asphalt Concrete

In general,acid aggregates are not used in combination with asphalt concrete because of their poor compatibility with the asphalt binder,which typically results in a scarce water stability of the concrete.In the present study,the feasibility of a new approach based on the combination of acid granite fine aggregate with alkaline limestone coarse aggregate and Portland cement filler has been assessed.The mineral and chemical compositions of these three materials have first been analyzed and compared.Then,the effect of different amounts of Portland cement(0%,25%,50%,75%and 100%of the total filler by weight)on the mechanical performance and water stability of the asphalt concrete has been considered.Asphalt concrete has been designed by using the Marshall method,and the mechanical performance indexes of this material,including the Marshall stability and indirect tensile strength(ITS),have been measured together with the related water stability indexes(namely the Marshall stability(RMS)and tensile strength ratio(TSR)).The results indicate that the alkaline limestone coarse aggregate and Portland cement filler can balance the drawback caused by the acid granite fine aggregate.The asphalt concrete has good mechanical performances and water stability when the amount of common limestone powder filler replaced by cement is not less than 75%.

Investigation of Carbonation of Concrete Based on Crushed Sand and Admixtures

Carbonation is a natural aging process that occurs in all types of concrete. One of its primary implications is the acceleration of steel corrosion caused by the phenomena of depassivation. The goal of this research is to investigate the carbonation of quarry sand-based concrete. The concrete is made of 100% crushed sand 0/6.3, gravel 8/15, and 15/25 from the Arab Contractor quarry in Nomayos, Cameroon, with CEM II B-P 42.5 R from CIMENCAM (Cimenteries du Cameroun). The study employed two admixtures: one with a dual superplasticizing and reducing action (Sikamen) and another with a water-repellent effect (Sika liquid). Carbonation was performed on concrete samples at the following dates: 0, 7, 14, 28, 56, 90, 180 days, one year, and six months. Carbonated concrete (CC) and non-carbonated concrete (NCC) samples are compared in terms of their physical attributes and mineralogical characteristics. The results of this investigation reveal that after more than a year and six months of carbonation, porosity decreases and permeability increases. Despite the high fineness modulus of quarry sand, the compressive strength of quarry sand-based concrete is satisfactory. Carbonation depth is relatively high on some dates, exceeding the minimal cover value for concrete reinforcement. Sikament additive increases concrete compactness and durability while decreasing permeability. Sika water repellant mixes with the lime in cement to generate complimentary crystallizations that block the mortar’s capillaries, making it watertight.

Effect of Hydration Aging and Water Binder Ratio on Microstructure and Mechanical Properties of Sprayed Concrete

In order to study the durability of sprayed concrete （shotcrete）, effects of different hydration aging and water-binder ratio （w/b） on the microstructure of cement paste and basic mechanical properties of test specimens were investigated. The phase composition, mass percentage of ettringite and portland in hydration production and microstructure were characterized by X-ray diffraction （XRD）, thermo gravimetry-differential scanning calorimetry （TG-DSC） and scanning electron microscopy （SEM）, respectively. The experimental results showed that changes in phase composition was more significant than those of water-binder ratio. With hydration aging and water-binder ratio increased, the mass percentage of ettringite and portland was decreased from 4.42%, 1.49% to 3.31%, 1.35%, respectively and the microstructure of paste was significantly compacted. Likewise, the mechanical properties including cubic compressive strength and splitting tensile strength were rised obviously.

Influence of subsequent curing on water sorptivity and pore structure of steam-cured concrete

Steam-cured condition is found to cause larger porosity and worse properties of concrete compared with normal curing condition. For the sake of seeking effective measurements to eliminate this bad effect of steam-cured condition on concrete, the water sorptivity and pore structure of steam-cured concretes exposed to different subsequent curing conditions were investigated after steam-curing treatment. The capillary absorption coefficient and porosity of the corresponding concretes were analyzed, and their mechanisms were also discussed. The results indicate that water sorptivity and pore structure of steam-cured concrete are greatly influenced by the curing condition used in subsequent ages. Exposure steam-cured concrete to air condition has an obviously bad effect on its properties and microstructures. Adopting subsequent curing of immersing steam-cured concrete into about 20℃ water after steam curing period can significantly decrease its capillary absorption coefficient and porosity. Steam-cured concrete with 7 d water curing has minimum capillary absorption coefficient and total porosity. Its water sorptivity is decreased by 23% compared with standard curing concrete and the porosity is 9.6% lower. Moreover, the corresponding gradient of water sorptivity and porosity of steam-cured concrete both decrease, thus mictostructure of concrete becomes more homogeneous.

Mechanical Properties of Sea Water Sea Sand Coral Concrete Modified with Different Cement and Fiber Types

The mechanical properties of modified sea water sea sand coral concrete(SWSSCC)under axial compression were experimentally studied.Two different parameters were considered in this test:types of cement and fiber.An experimental campaign was developed involving uniaxial compression tests and the use of digital image correlation(DIC)method to analyze the strain distribution and crack propagation of specimen.Test results indicated that the compressive strength and elastic modulus of SWSSCC were improved by adding stainless steel fibers(SSF),while polypropylene fibers(PF)enhanced the SWSSCC peak deformation.It was found that the elastic modulus and strength of SWSSCC using ordinary Portland cement(OPC)were higher compared to specimen with low alkalinity sulphoaluminate cement(LAS).Typical strain distribution changed with the variation of fiber types.The propagation and characteristics of cracks in SWSSCC containing PF were similar to those of cracks in SWSSCC.However,the propagation of cracks and the development of plastic deformation in SWSSCC were effectively hindered by adopting SSF.Finally,an analytical stress-strain expression of specimen considering the influences of fibers was established.The obtained results would provide a basis for the application of SWSSCC.

Properties of Sustainable High Strength Concrete with Waste Copper Slag

The present work investigates copper slag as a substitute for river sand in high-strength concrete.The concrete mixtures were manufactured with 10%,30%,50%,70%,and 100%of copper slag to evaluate the mechanical and durability properties.The experimental results indicate that replacing copper slag above 50%affects the performance characteristics of the concrete due to its high angularity and lower water absorption characteristics.The strength of concrete with 50%copper slag is improved by 5.6%,whereas the strength of concrete with 100%copper slag is reduced by 2.75%at 28 days.However,increased curing to 90days improves the strength of the former by 7.16%and reduces the latter by only 0.23%.The water absorption,porosity,and rapid chloride penetration of the concrete mixtures with 100%copper slag are increased by 10.44%,13.20%,and 19.56%compared to control concrete.Micro-structural investigations through SEM infer higher replacement of copper results in higher void formation due to its reduced water absorption.

Effect of Alkaline Electrolyzed Water on Performance Improvement of Green Concrete with High Volume of Mineral Admixtures

The strength and durability of concrete will be significantly reduced at high volume of mineral admixture,and the poor early strength of concrete also still needs to be solved.In this investigation,a highly active alkaline electrolyzed waters was used as mixing water to improve the early strength and enhance the durability of green concrete with high volume mineral admixture,the influences of alkaline electrolyzed water(AEW)on hydration activity of mineral admixture and durability of concrete were determined.The results showed that compared with natural tap water,AEW can accelerate early hydration process of cement in concrete and produce comparatively more hydrated products,leading to a 13.6%higher compressive strength than that of ordinary concrete at early age,but the improvement effect of AEW concrete was relatively reduced at long-term age.Meanwhile,the activity of mineral admixtures could be stimulated by AEW to some extent,the strength and durability performance of AEW concrete after double doping 25%slag and 25%fly ash can still reach the level of ordinary cement concrete without mineral admixtures.The SEM micromorphology of 7 d hydrated natural tap water cement paste was observed to be flaky and tabular,but the AEW cement pastes present obvious cluster and granulation phenomenon.The SEM microstructure of AEW concrete with mineral admixtures is more developed and denser than ordinary tap water concrete with mineral admixtures.Therefore,the AEW probably could realize the effective utilization of about 50%mineral admixture amount of concrete without strength loss,the cement production cost and associated CO_(2) emission reduced,which has a good economic and environmental benefit.

Additional water use influencing strength and fluidity of recycled concrete

Through adding different additional water use,the compressive strength,splitting tensile strength and fluidity of recycled concrete of three aggregate combination forms were studied by experiment respectively.The experimental results show that with the increase of adding additional water use,the compressive strength and splitting tensile strength of recycled coarse aggregate concrete decrease,but that of recycled fine aggregate concrete and recycled all aggregate concrete increase firstly then decrease.When additional water use is added more 15% or 20% than that of basic ordinary concrete,the recycled coarse aggregate concrete and fine one can get pretty good fluidity.When it is added more 30%,the recycled all aggregate concrete has fluidity that is just satisfied.

Quality Improvement of Recycled Concrete Aggregate by Accelerated Carbonation under Different Pressure

Due to the presence of old mortar (OM) and interfacial transition zone (ITZ),recycled concrete aggregate (RCA) is inferior to natural aggregate (NA).The purpose of this paper was to study the effect of accelerated carbonation on the macro-properties and micro-properties of RCA under different pressure(0.05,0.15,0.30 MPa).The macro-property tests included colour change,apparent density,water absorption,and crushing value of RCA.The micro-property tests included scanning electron microscopy (SEM),X-ray diffraction (XRD),thermogravimetry-differential scanning calorimetry (TG-DSC),and Vickers micro-hardness(VMH).The results showed that the change trends of apparent density,water absorption,and crushing value of RCA displayed exponential relationships as pressure increasing,with the optimum pressure of 0.30 MPa.SEM images indicated that the calcite caused by the hydration products in RCA and the Ca(OH)_(2) derived from saturated lime water improved the properties of RCA;as the apparent density increased,the water absorption and crushing value decreased.The results of XRD and TG-DSC indicated that,as the pressure increased,the masses of Ca(OH)_(2) in carbonated RCA gradually decreased,while those of CaCO_(3) gradually increased,which demonstrated that the carbonation degree gradually increased.Besides,ITZ-2 was the weakest phase in RCA,but its improvement degree of VMH by accelerated carbonation was higher than that of OM.However,RCA was not completely carbonated,but only carbonated in a certain depth after 24 h accelerated carbonation.

Non-Contact Terahertz Inspection of Water Content in Concrete of Infrastructure Buildings

Concrete is the most widely used for construction materials in the world. Water content of concrete is an important parameter in terms durability of concrete structures. Terahertz (THz) waves, for which concrete is a porous and absorbable material, have been studied in order to establish a new non-contact inspection technology for maintenance of concrete structures. In this study, THz transmittance and reflectance of concrete in drying process were measured with a 60 GHz GUNN diode and absorption coefficient is analyzed for concrete with various water contents. It is shown that quantitative detection below 10% is possible for the water content at surface area of concrete.

Analysis of the Performances and Optimization of Polyurethane Concrete with a Large Percentage of Fly Ash

The properties of polyurethane concrete containing a large amount of fly ash are investigated,and accordingly,a model is introduced to account for the influence of fly ash fineness,water ratio,and loss of ignition(LOI)on its mechanical performances.This research shows that,after optimization,the concrete has a compressive strength of 20.8 MPa,a flexural strength of 3.4 MPa,and a compressive modulus of elasticity of 19.2 GPa.The main factor influencing 28 and 90 d compressive strength is fly ash content,water-binder ratio,and early strength agent content.

Water Absorption and Chloride Ion Penetrability of Concrete Damaged by Freeze-thawing and Loading

In order to investigate water and chloride ion transport in damaged concrete, three types of concrete were prepared, freeze-thawing（F-T） cycling and compressive loading were adopted to induce damage to concrete. Ultrasonic pulse velocity technique was used for evaluating the damage degree of concrete, and the defects of damaged concrete were also detected by X-CT. Water absorption and chloride ion penetrability were used for describing the transport properties of damaged concrete. Effects of damage degree on the water absorption rate and chloride ion penetrability were investigated in detail and the relationships were also established. The results show that the water absorption of concrete makes various responses to damage degree due to the difference of concrete type and damage method. For same concrete with similar damage degree, the water absorption rate of F-T damaged concrete is usually larger than that of concrete damaged by loading. The chloride ion penetrability of damaged concrete increases linearly with increasing damage degree, which is more sensitive to damage degree if the original penetrability of sound concrete is higher.

Experimental Evaluating of the Physical, Mechanical and Durability Properties of Natural, Recycled and Both Combined Aggregates Based Concretes

This experimental study aims at the reuse of recycled aggregates (RA), resulting from the demolition of concrete, cement block and cement mortar, in the manufacture of common construction in Burkina Faso. The RA can readily replace natural aggregates in concrete. Then five formulations of natural and recycled aggregates based concrete for characteristic strength of 25 Mpa were prepared in addition to the natural aggregates base concrete named reference concrete (BN): two types of recycled aggregates concrete (BR), three types of recycles and natural combined aggregates base concrete (BC). The properties of natural and recycled aggregates were characterized and the physical, mechanical strength and durability properties were also evaluated for all concrete specimens. All the studied concrete formulation present a density between 2000 kg/m3 ≤ ρ ≥ 2600 kg/m3 and an average slump of 4.9 ± 0.1 cm. The obtained results indicate that the recycled aggregates are suitable for current concrete. Two out of the five combinations studied, such as the natural (BN) and combined aggregate (BC2) based concretes satisfy the mechanical characteristics (Rc28 > 25 MPa) at 28 days of age and an average absorption coefficient of 2.93% and 3.98%. The recycled aggregate based concrete (BR1, BR2) and combined aggregate based concrete (BC1), gave respective average compressive strength of 21.55 MPa, 20.50 MPa and 20.30 MPa, i.e. a difference of 13.80% to 18.80% under the characteristic strength (25 MPa) aimed at 28 days of age. Thus, the recycled aggregates are in conformity with the normative prescriptions and their use for standard concrete gives adequate physical, mechanical and durability properties for the production of the C20/25 concrete series in the common civil engineering applications.

Water Permeability in Fly Ash-Based Geopolymer Concrete

This research investigated the water permeability coefficient of fly ash-based geopolymer concrete. The effect of sodium hydroxide （Na（OH）） concentrations and Si/AI ratios on water permeability and compressive strength of geopolymer concretes were studied. The geopolymer concrete were prepared from Mae Moh fly ash with sodium silicate （Na2SiO3） and sodium hydroxide （Na（OH）） solutions. In the first group, concentration of Na（OH） was varied at 8, 10, 12, and 14 molar and the Si/AI ratio was kept constant at 1.98. In the second group, a concentration of Na（OH） was kept constant at 14 molar and the Si/AI ratio was varied at 2.2, 2.4, 2.6, and 2.8. The hardened concretes were air-cured in laboratory. The compressive strength and water permeability were tested at the age of 28 and 60 days. The results showed that compressive strengths of geopolymer concrete significantly increased with the increase of a concentration of Na（OH） and Si/AI ratio. The water permeability coefficients increase with the decrease of compressive strength. In addition, the high reduction of water permeability coefficients with time was found in geopolymer concrete with lower Na（OH） concentration than that higher Na（OH） concentration.

Internal Curing Using Water-releasing Material for High Strength Micro-expansive Concrete

Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this problem, water-releasing material with water storage and releasing characteristics was incorporated into high strength micro-expansive concrete to provide internal curing, and expansive effect of expansive agent was improved. Migration of water from initially saturated water-releasing material to the surrounding hydrating cement paste was investigated. Based on a given efficient diffusion distance of water stored in water-releasing material, the mass and real water-cement ratio of cured cement paste were estimated. At the same time, the effect of internal curing of water-releasing material on the volume deformation of high strength micro-expansive concrete was investigated.

Effects of Curing Methods on the Permeability and Mechanism of Cover Concrete

Curing methods are one of the most important factors in determining the quality and compactness of cover concrete.The effect of curing methods on the water absorption and sorptivity coefficient of cover concrete with the substitution ratio of fly ash(FA)and ground granulated blast slag(GGBS)for cement between 30 wt%and 40 wt%was studied by capillary water absorption test.The vacuum saturation test and mercury intrusion test were employed to characterize these differences in the pore structure of cover concrete under different curing methods.With further analysis of the compactness of microstructure by SEM,the mechanism of the impact of curing methods on the permeability of cover concrete was revealed.The results obtained indicate that the effect of curing methods on the water absorption,sorptivity coefficient and porosity of cover concrete shows the trend of natural curing>cover curing>water curing>standard curing.It is also shown that reasonable curing is advantageous to reduce the porosity and permeability of cover concrete.In natural curing conditions,the appearance of porosity increasing and pore structure coarsening is more critical for covering concrete with mineral admixtures than for pure cement concrete.Therefore,the permeability of cover concrete with mineral admixtures is more sensitive to the early-age curing methods.

Thermal field in water pipe cooling concrete hydrostructures simulated with singular boundary method

The embedded water pipe system is often used as a standard cooling technique during the construction of large-scale mass concrete hydrostructures. The prediction of the temperature distribution considering the cooling effects of embedded pipes plays an essential role in the design of the structure and its cooling system. In this study, the singular boundary method, a semi-analytical meshless technique, was employed to analyze the temperature distribution. A numerical algorithm solved the transient temperature field with consideration of the effects of cooling pipe specification, isolation of heat of hydration, and ambient temperature. Numerical results are verified through comparison with those of the finite element method, demonstrating that the proposed approach is accurate in the simulation of the thermal field in concrete structures with a water cooling pipe.

The Impact of Marine Water on Different Types of Coarse Aggregate of Geopolymer Concrete

This research studies the impact of different types of coarse aggregate on the behavior of geopolymer concrete based on both fly ash (FA) and ground granulated blast furnace slag (GGBFS) in different marine environments. Aiming to solve the problems caused by the construction and demolition waste and the depletion of natural aggregates, in the present study coarse recycled aggregates is used to produce new green concrete with a fly ash-slag based geopolymer. By this examination, the research seeks to improve the quality and productivity of concrete used in construction and hydraulic projects. For this research, four mixtures containing different types of coarse aggregate in two different water environments were used. The utilized mixtures contained natural aggregate concrete (NAC) such as basalt and crushed marble. Also, recycled coarse aggregate concrete (RAC), which totally replaced natural aggregate, was presented in this paper such as crushed concrete and crushed ceramic. For this study, in the sieve analysis;specific and unit weights, was recorded. Furthermore, the mechanical properties were determined, using a compressive test that was conducted on the 7th, 28th, 56th and 90th days at different water environments;potable water (PW) and sea water (SW). Durability test was also performed for total absorption measurement. Results indicated that geopolymer concrete exhibits better strength in marine environments than in those of potable water. Results also showed that crushed marble (CMA) exhibits higher compressive strength and durability.